28 October 2010

Growing big brains

We think that good environments make for good brains, particularly when people are young. Parents have been known to obsess a little about whether their kid is getting the right kind of experiences.

If this is true, this guy must have read a looooooot of books.

Joking aside, we normally think about early experiences as influencing subtle things about the brain. Those early experiences might give you some extra connections, tweak a little wiring here and there. But would you expect someone’s brain to get significantly bigger, a la The Leader?

Brain size is normally the domain of comparative vertebrate neuroanatomists rather than developmental psychologists. It’s actually a major preoccupation for comparative neuroanatomists, who typically trying to explain differences in brain size of different species, usually by relating some aspect of brain size to the differing ecology and behaviour patterns of those species.

But that differing ecology might not only affect brain sizes of different species, but brain size within the same species: individuality.

We know that being in natural environments can affect the formation of new neurons (here). It’s less clear if that could make for significantly bigger brain regions, or overall brain size, though. And “lab versus wild” is a fairly crude comparison. It would be nice to narrow down to a couple of relevant ecological factors.

Gonda and colleagues are working on this problem with these little guys and gals:

These are tadpoles for Rana temperaria, a fairly common frog in Europe. The experiments are pretty simple. Divide up a group of tadpoles into four tanks, a simple two by two matrix:

Half the tanks with predators (contained, so it could not eat the tadpoles) and half without.

Half with 50 tadpoles and half with 10.

Let simmer for three and a half weeks. Then, check bodies and brains.

Tadpoles in low densities grew larger than those in high densities; predators also made for smaller tadpoles. All tanks were given the same amount of food per tank, not the same amount of food per capita, so this may just reflect food availability.

Brain size is more complicated. The smallest brains were in animals kept in low densities with predators. This is a bit of a surprise, since one might expect that little competition would mean more food for brain growth. Different effects occurred at different brain regions, too. The authors say, “tadpoles had relatively larger optic tectum and smaller medulla oblongata at high tadpole density.” This suggest these two regions have different roles in processing the cues that occur in high versus low density situations.

How general might ecological effects on brain development be? I wonder if the amount of plasticity might be greater in amphibians than many other animals. Amphibian tadpoles may be particularly liable to have their brains reshaped. They grow fast, and their brains still have to undergo a metamorphosis. These factors might make tadpole brains more plastic than species where the little one are basically miniature adults.